Problem: Simplify the following expression: $k = \dfrac{30st + 20t}{30t^2} - \dfrac{15rt + 30t^2}{30t^2}$ You can assume $r,s,t \neq 0$.
Explanation: Since the expressions have the same denominator we simply combine the numerators: $k = \dfrac{30st + 20t - (15rt + 30t^2)}{30t^2}$ $k = \dfrac{30st + 20t - 15rt - 30t^2}{30t^2}$ The numerator and denominator have a common factor of $5t$, so we can simplify $k = \dfrac{6s + 4 - 3r - 6t}{6t}$